1. Field of the Invention
The present invention relates to a monitoring device for monitoring a connection between respective electronic control units (ECU) on a vehicle and power lines for supplying power to the ECU (ECU monitoring device hereinafter).
2. Description of the Related Art
Recently, there is a growing trend of vehicles equipped with antitheft systems (immobilizer systems) as measures for recent rash of stealing vehicles.
In general, an immobilizer system includes an ignition key having a transponder built-in, an immobilizer ECU, an engine ECU and so on. In operation, the immobilizer system is constructed so as to judge whether or not a vehicle is being used falsely by transmitting/receiving a code signal among the above constituents. Such a constitution is disclosed in Japanese Patent Publication Laid-open No. 8-30873.
However, if both or either one of the immobilizer ECU and the engine ECU is replaced by another instrument, then the immobilizer system breaks down. That is, it means that the immobilizer system cannot detect a vehicle being improperly used, so that it becomes impossible to protect the vehicle against theft.
In such a situation, it has been desired to provide a system of detecting a point of time when either the immobilizer ECU or the engine ECU is detached from the vehicle falsely and further informing a passenger of the vehicle or its circumference of such a false detachment. As this type of system, various monitoring systems shown in FIGS. 1 to 3 are known conventionally.
In the monitoring system of FIG. 1, a junction box (J/B) ECU 101 is connected to an immobilizer ECU 102 through an exclusive line L101. In operation, by measuring a voltage level of the exclusive line L101, it is judged whether or not the immobilizer ECU 102 is connected to the junction box (J/B) ECU 101. In detail, if the voltage of the line L101 is at a low level, it is judged that the exclusive line 101 is in the normal connection. While, if the voltage of the line L101 is at a high level, it is judged that the immobilizer ECU 102 is disconnected from the junction box (J/B) ECU 101 falsely.
In the above monitoring system of FIG. 1, however, the system is apt to be large-sized due to the need of providing the exclusive line L101 for monitoring the connection, causing the installation cost to be elevated. Additionally, since the same system is formed so as to detect a direct-current (DC) voltage, it is untreatable to a thieving procedure of first connecting the line L101 to a ground and subsequently detaching the immobilizer ECU 102 from the system. Thus, since the voltage of the exclusive line does not exhibit a high level, it is possible to detect that the immobilizer ECU 102 has been detached from the system.
In the monitoring system of FIG. 2, the junction box (J/B) ECU 101 is connected to the immobilizer ECU 102 through a power line L102. In operation, by measuring a dark current flowing the power line L102, if a value of the dark current is a few (μA), it is judged that the immobilizer ECU 102 is in the normal connection. While, if a value of the dark current is 0 (μA), it is judged that the immobilizer ECU 102 is disconnected from the junction box (J/B) ECU 101 falsely.
In the above monitoring system of FIG. 2, however, since a current to be detected is remarkably small, there is the possibility of misjudgment, raising a problem of the impossibility of detection with high accuracy.
In the monitoring system of FIG. 3, the junction box (J/B) ECU 101 is connected to the immobilizer ECU 102 through a CAN communication line L103. In operation, if the communication line L103 is connected between the junction box (J/B) ECU 101 and the immobilizer ECU 102 normally, then it is judged that the CAN communication is being performed normally. While, if the communication line L103 is cut off, it is judged that the immobilizer ECU 102 is detached from the system due to disruption in communication.
However, since the above system adopts the standard protocol communication, there is the possibility that if the system is operated with the use of a commercial instrument falsely, it becomes impossible to detect that the immobilizer ECU 102 has been detached.
As mentioned above, the conventional monitoring systems for ECU mounted on a vehicle have various problems. Commonly, there exists a drawback that it is impossible to detect that the immobilizer ECU 102 has been detached from the system, with high accuracy.